Vibratory forming

ABSTRACT

A vibratory forming method, and apparatus, in which material is drawn across a pair of forming tools which are both vibrated. The phase angle between the two vibrations is neither zero nor 180*, but is adjusted to a defined intermediate value to increase the efficiency of the process, especially by minimising the drawing force required. The invention applies particularly to the plug drawing of metal tube.

United States Patent [191 Dawson et al.

[ VIBRATORY FORMING [75] Inventors: Graham Robert Dawson, Bewdley;

Dennis Hugh Sansome, Sutton Coldfield, both of England [73] Assignee:National Res earch li el opnien? Corporation, London, England [22]Filed: Mar. 17, 1972 [21] Appl. No.: 235,546

[30] Foreign Application Priority Data Mar. 18, 1971 Great Britain7201/71 [52] US. Cl 72/283, 72/56, 72/DlG. 20,

, 72/285 [51] :Int. Cl B21d 26/02, B2lc H24 [58] Field of Search 72/DIG.20, 274,

[56] References Cited UNITED STATES PATENTS Boyd et al 72/1310. 20

[ Jan. 1974 10/1965 Boyd et al 72/DIG. 2O l/l946 Vang 72/D1G. 20

Primary Examiner-Charles W. Lanham Assistant ExaminerM. J. KeenanAttorney-Cushman, Darby & Cushman [5 7 ABSTRACT A vibratory formingmethod, and apparatus, in which material is drawn across a pair offorming tools which are both vibrated. The phase angle between the twovibrations is neither zero nor 1 80, but is adjusted to a definedintermediate value to increase the efficiency of the process, especiallyby minimising the drawing force required. The invention appliesparticularly to the plug drawing of metal tube.

3 Claims, 14 Drawing Figures PATENTEDJAH 81% $783,668

SHEET 1 [IF 5 VIBRATORY FORMING This invention relates to the reductionof metals and other materials by drawing them past at least two tools.In particular it relates to drawing metal rod through a succession ofdies, first coarse and then fine, and to drawing tube through theclearance between a female die and a male die, the latter beinggenerally known as a plug. It has already been proposed, in plugdrawing, to vibrate both the die and the plug axially while drawingproceeds; see for example U.S. Pat. No. 3,212,312, corresponding to UKNo. 1,075,331. However, although such documents refer generally to thepossibil-. ity of varying the relationship between the vibrations of theplug and those of the die, and have specifically mentioned thepossibilities that such vibrations could be in-phase or 180out-of-phase, they did not suggest how to set about an analysis of thisrelationship nor of course the optimum values that such an analysismight reveal.

We have now devised and carried out such an analysis. It is summarisedlater in this specification and leads to the surprising conclusion thatoptimum performance is in certain cases achieved when the phase anglebetween plug and die is neither nor 180 but is somewhere between thetwo, the value depending upon several factors peculiar to the case.

Broadly speaking our invention includes vibratory forming operationsusing a pair of vibrating tools in which the phase relationship betweenthe tools is substantially the optimum which will be described. Ourinvention includes apparatus set to achieve such optimum performance.

The invention is formally defined by the claims at the end of thisspecification and will now be described, by

way of example, with reference ot the accompanying drawings in which:

FIG. 1 is a diagrammatic side elevation of suitable apparatus,

FIGS. 2a. to 2f. illustrate the relative positions of die and tube atsix stages of a cycle of die oscillation,

FIGS. 3 and 4 are graphs showing typical relationships between importantparameters discussed in the analysis, and

FIGS. 5 to 9 aregraphs in which other parameters from the analysis areeach plotted against time.

FIG. 1 shows an input or original metal tube 1 being reduced to a finaltube 2, of smaller internal and external diameter, by being drawnthrough the clearance 3 between a male die or plug 4 and a female die 5.The tube is drawn through this clearance by gripping jaws 6 mounted on adrawing device (not shown) which supplies the drawing force and moves inpace with the drawn tube. Plug 4 is mounted, as is usual, on a plug bar7. This bar is supported from a plug vibrator 8, which imparts axialvibrations to bar and plug. Female die 5 is connected to a die vibrator9, which imparts co-axial vibrations to the die, and vibrators 8 and-9are linked to a control device 10 which controlsthe relative phase ofthe two vibrations.

Drawing takes place whenever there is relative movement between tube llandthe die 5. Using known apparatus the drawing force, i.e., the forcerequired to reduce the tube by pulling it through the die and plug wouldneed to exceed the sum of two other forces. The first of these would bethe die force, i.e., the force with which the outer surface of theoriginal tube resists being pulled and deformed through the die. Thesecond would be the plug force, i.e., the frictional force created bypulling the inner surface of tube 1 over the plug 4. By moving the plugat the same speed as the final tube 2 during drawing, and in the samesense, the plug force disappears and so the drawing force has only toexceed the die force. lBy moving the plug faster than the tube the plugforce actually contributes to the drawing force, so that the drawingforce then equals the difference between the die and plug forces, nottheir sum. Since the maximum reduction in area that can be brought aboutin the original tube 1 varies as the tensile strength of the final tube2, it is important to keep the maximum drawing force low and thisinvention shows a way of doing this. By moving the plug faster than thefinal tube, the drawing force may be decreased by twice the plug forceand still draw at the same rate as before. This can represent a 60percent gain in machine capacity since the plug force can equal 30percent of drawing force.

FIG. 2, parts a to f, illustrates the relative motion of final tube 2and female die 5 during a typical drawing operation. Reference Arepresents the amplitude of oscillation of the die. Part 2a shows die 5at the extreme rearward end of its strokerelative to the direction 11 inwhich the tube is being drawn. At this stage drawing is taking place,that is to say there is such tension in the tube that it is movingthrough the die from left to right. In part 2b the oscillation of thedie has started it moving again towards the right; tension in the tubeis still sufficient to cause drawing at the die, but the motion of thedie means that the velocity of the tube through the die is less thanbefore, and is diminishing. Part 2c shows the point in time wheredrawing stops because the relative velocity has dropped to zero. Fromnow until the moment illustrated in part 2f there is no relativemovement between die and tube, and thus no draw. Part 2d shows the dieat the extreme right hand or forward end of its stroke; since the momentshown in part 20, the further motion of the die 5 has tended to diminishstill further the tension in the final tube 2. Part 2e shows the die onthe backward stroke of its oscillation, building up the tension again inthe drawn tube, and part 2f illustrates the point in time when thetension has again reached the level necessary to cause drawing. Becauseof the many variable factors that contribute to the tension in the finaltube 2, the positions of the die in parts 2c and 2f are not necessarilythe same. Nevertheless, since drawing starts at the position shown inpart 2f and continues until a position corresponding to part 2c is nextreached, the present invention aims at so relating the vibrations ofplug 4 and die 2 that the plug 4 is at 1 6 relative movement of ends oftube during period of elastic loading and offloading F non-oscillatorydrawing force AF non-oscillatory plug force f oscillatory drawing forcefp oscillatory plug force Suffices 1. Die 2. Tub at die 3. Other end oftube (i.e., at gripping jaws 6) 4. Plug The following assumptions havealso been made:

I. The magnitude of the plug force is unaltered by its periodic reversal(fp :AF) 2. The deformation pattern is unaltered by the reversal of plugforces (f.max F2AF) 3. Inertia forces in the tube are negligible 4. Thedrawing velocity is constant (no periodic component due to the cyclicforces imposed) 5. The drawing force exerted by jaws 6 is constant. Attime t let the die be at its most backward position and let the plughave a phase lead of 0/2 0 over the die. Furthermore assume drawing tobe occurring. Thus:

x, A cos wt (1) x.,=B sin (wt+6) (2 and until drawing stops x, x, V,since the drawing force is constant. Drawing will stop when the relativevelicity of tube and die reaches zero, at t t,.

i.e., when x, x, 0

i.e., v Aw sin wt, 0

Thus drawing stops at t t, where Fromthis time, since drawing hasstopped, the tube at the die will follow the die, whilst the other endwill have a constant velocity V. This will result in a period of elasticoffloading and loading. During this period:

where x, V, and

x, x, Aw sin wt.

Thus 8 A cos wt, A cost wt V (t, t).

Drawing will restart when the drawing force felt at the die returns tothat exerted at 6 (see FIG. 6 becomes zero at t 1,, where from above:

A cos wt, Vt, A cos wt, Vt,.

Combining with (3), this gives:

A cos wt, Vt, A cos d: V/w 4 During the drawing period determined above,the velocity of the plug relative to the tube must be zero or in thepositive direction throughout, if the forces are to be reduced. Thisperiod of reversed friction has a maximum of 21r/w, for zero drawingspeed, and reduces with increasing drawing speed. The system isoptimised when the period of reversed friction isequal in duration tothe drawing period and is synchronised with it, since no furtherincrease in speed may be tolerated without reverting to the conventionaldrawing force. This corresponds to friction reversing at t t, and t,.Thus:

at t I i, i and V Bw cos (wt, 0).

cos (wt, 0) V/nAw sinln (from (3)) .-.n sinlcos 5 0) (5) and at t t,,

it, x,, and cos (wt, 0) sinln as above.

wt, 0 cos" sinda/n or 211' cos sinda/n where cos" sinda/n 1r Since wt,does not equal wt, the second solution is correct.

wt, 2'rr 6 cos" sin/n Equation (8) expresses the optimum phase angle fora give value of d). This was solved by plotting the right hand sideagainst the left for a range of values of 4:, each with a range ofvalues of 0 and interpolating the correct 6. FIG. 3 gives the variationof optimum phase angle with velocity ratio, sindz. FIG. 4 gives thevariation of the corresponding value of amplitude ratio, n, withvelocity ratio, sinda. This expresses the minimum value of plugamplitude necessary for friction reversal or at least elimination tooccur throughout the drawing period, when the optimum phase angle isused.

FIGS. 5 9 illustrate several realtionships referred to in the aboveanalysis.

Another important quantity is the velocity ratio, sinda, that is to saythe ratio between the drawing speed V and the angular velocity of theoscillation of female die 5. Now for there to be reversed motion, or inthe limiting case no relative motion at all between plug and diethroughout the drawing period, the drawing interval must not exceed onehalf cycle or 1r.

Now friction reverses when t 1,, i.e., where wt, d: sin"V/Aw Frictionalso reverses when t t, where A cos Vlw= A cos wt, Vt,.

In the critical condition wt, 1r wt, 1r d).

.'.sin.max 0.5370 (V/Aw).max 9 This in effect limits the process atpresent to drawing speeds of up to 500 feet per minute, because of thelimit to the oscillatory velocity that can be obtained with currentvibrators conveniently available. I

The above analysis gives data to optimise the process. The main factorsare:

(1 For a velocity ratio (V/Aw) in excess of 0.537 the process isineffective.

(2) For a velocity ratio less than that there is an optimum phase anglebetween die and plug oscillations.

(3) At this velocity ratio, and with the optimum phase angle, there is aminimum amplitude ratio (n) below which the process is ineffective.

(4) At the optimum phase angle, drawing velocity is maximised, all elsebeing held constant, or the plug amplitude is minimised, all else beingheld constant.

If, in an actual process the phase angle and amplitude ratio are setcorresponding to a high value of velocity ratio, sin, there remains thequestion: is the process effective for lower values of 11, whichcorrespond to low speeds encountered when drawing is initiated. Now forlower values of the optimum phase angle 6 is reduced. Thus if 0 is heldconstant, optimised for a high value of 11, and d) is reduced, then thedrawing period occurs later, and the reversed friction period remainsunmoved. If n, and hence the plug ampltiude, is reduced, then theinstant of friction reversal will coincide first with the instant whendrawing stops. This condition is said to be critical since any furtherreduction of n will result in drawing at a higher load.

Now:

x -A cos wt x B sin (wt 0) as before, but 6 constant.

Drawing stops when:

Aw sin wt V wt sin V/Aw The critical value of n is given Bw cos (wt, 0)V This gives the critical value for n for both the high, optimised valueof (b, and for those values below. The process is said to be effectiveif ncontinually reduces with so that the critical value at the optimisedcondition is always in excess of that corresponding to lower values ofdz.

This is so if dnld 0 for the whole range.

NOW dnld cos (d) 0) cos sin sin (qS But from FIG. 4 0 0 58 30' and thusthe process is effective for speeds upto the optimum condition.

Although described with relation to apparatus and a process for the plugdrawing of tube, the invention is applicable also to other apparatusandv processes in which material is passed through several tools. Byoscillating these tools at the correct phase angle a reduction in totaldrawing force can be achieved by operating one tool to causeintermittent deformation and operating the other with such phase thatfrictional constraint by that tool upon the deformation eitherdisappears or is reversed. This can apply to many known processes inwhich deformation is associated with two tools, e.g., deep drawing. Insuch applications, of course, the limiting valves for velocity ratio,amplitude ratio etc. may be different but may be determined by similaranalysis.

Extra effects will also have to be taken into consideration if thesecond tool exerts not only the frictional constraint of theparallel-sided plug described in this specification. For instance thesecond tool could also deform to some extent.

It should also be noted that the vital related vibrations to which thisinvention applies are those at the die and at the plug. It is normallynot difficult to position the die vibrator (9) close to the die itself(5) so that the vibrations of the vibrator are very similar in time andall other respects to those at the die itself. However, vibrations canonly be transmitted to the plug through the plug bar 7. This bar, whichmay be quite long, will ensure that the vibrations of the plug do notcorrespond with those of vibrator 8. Vibrator 8 must therefore be set sothat not its own vibrations, but those at the other end of the bar, arecorrect. The difference will tend to be the greater the lower thefrequency of the vibrations, e.g., if they are in the sonic range.

It is also unnecessary, although often simpler for the purposes ofanalysis, that the vibrations should be sinusoidal. They may be of othertypes, provided the phase angle between die and plug can be practicallyascertained.

We claim:

ll. A method for vibratory forming in which material is drawn across atleast one pair of tools, in which each tool of the pair is vibratedaxially while drawing proceeds, and in which the phase angle between thetwo vibrations is such that while the material is drawing relative toone of the pair of tools the other tool has a velocity no lower thanzero, relative to the material, in the direction of drawing.

2. A method for vibratory forming according to claim 1 inwhich a tube isdrawn through a clearance between said pair of tools, comprising afemale die and a male plug, and in which the equation:

Sin0Cot+Cos0=0/Sin0 is satisfied, where the phase lead of the plugoverthe die is rrl2+0 and where =2Sin V/Aw, being the drawing speed, A theamplitude of the vibrations of the die and w their angular frequency.

3. Plug drawing apparatus for drawing metal tube comprising a female dieand a male plug defining an annular orifice through which the tube isdrawn axially, first means to vibrate both die and plug in a directionparallel to said axis, and second, adjustable means controlling'therelationship between the vibrations of said die and said plug, saidsecond means being so set that the equation:

Sin 0Cot+Cos 0=0/Sin 0, is satisfied where rt-l2 0 is the phase lead ofthe vibrations of the plug over those of the die and where d) SifV/Aw, Vbeing the drawing speed, A the amplitude of the vibrations of the dieand w their angular frequency.

1. A method for vibratory forming in which material is drawn across atleast one pair of tools, in which each tool of the pair is vibratedaxially while drawing proceeds, and in which the phase angle between thetwo vibrations is such that while the material is drawing relative toone of the pair of tools the other tool has a velocity no lower thanzero, relative to the material, in the direction of drawing.
 2. A methodfor vibratory forming according to claim 1 in which a tube is drawnthrough a clearance between said pair of tools, comprising a female dieand a male plug, and in which the equation: Sin theta Cot phi + Costheta - theta - phi /Sin theta is satisfied, where the phase lead of theplug over the die is pi /2 + theta and where phi 2Sin 1V/Aw, V being thedrawing speed, A the amplitude of the vibrations of the die and w theirangular frequency.
 3. Plug drawing apparatus for drawing metal tubecomprising a female die and a male plug defining an annular orificethrough which the tube is drawn axially, first means to vibrate both dieand plug in a direction parallel to said axis, and second, adjustablemeans controlling the relationship between the vibrations of said dieand said plug, said second means being so set that the equation: Sintheta Cot phi + Cos theta - theta - phi /Sin theta , is satisfied wherepi /2 + theta is the phase lead of the vibrations of the plug over thoseof the die and where phi Sin 1V/Aw, V being the drawing speed, A theamplitude of the vibrations of the die and w their angular frequency.